Phenylcyclohexanes and a liquid-crystalline medium

ABSTRACT

Novel phenylcyclohexanes of the formula I 
                 
 
in which n is 0 to 7, Q 1  and Q 2  are H, or one of these radicals is alternatively CH 3 , r is 0, 1, 2, 3, 4 or 5, A is trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or a single bond, X is F, Cl, —CF 3 , —CN, —OCF 3  or —OCHF 2 , and Y and Z are each, independently of one another, H or F, with the proviso that, in the case where A is a single bond, Q 1 =Q 2 =H and simultaneously X=CN, Y and/or Z are F.

This application is a continuation of U.S. Ser. No. 09/686,816, filedOct. 12, 2000, abandoned, which is a divisional application of U.S. Ser.No. 08/486,228, filed Jun. 7, 1995, now U.S. Pat. No. 6,284,154, whichis a continuation application of U.S. Ser. No. 08/046,286, filed Apr.15, 1993, now U.S. Pat. No. 5,891,360, which is a divisional of U.S.Ser. No. 07/585,165, filed Oct. 16, 1990, now abandoned.

The invention relates to novel phenylcyclohexanes of the formula I

in which n is 0 to 7, Q¹ and Q² are H, or one of these radicals isalternatively CH₃, r is 0, 1, 2, 3, 4 or 5, A istrans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or asingle bond, X is F, Cl, —CF₃, —CN, —OCF₃ or —OCHF₂, and Y and Z areeach, independently of one another, H or F, with the proviso that, inthe case where A is a single bond, Q¹=Q²=H and simultaneously X=CN, Yand/or Z are F.

EP-A 0 122 389 discloses similar compounds, for example of the formula A

However, these compounds do not satisfy all the demands, in particularwith respect to (long-term) stability, for example for use in displayshaving an active matrix.

German Offenlegungsschrift 29 07 332 discloses similar compounds of theformula

These nematogenic compounds are preeminently suitable for improving thelow-temperature behavior of nematic mixtures, but, on the other hand,have relatively high values for the vapor pressure at small values of n.

EP-A 0 280 902 discloses similar compounds of the formula

in which A is F, Cl, Br, H or CN. Although these compounds have lowvalues for the vapor pressure, they have, on the other hand, clearlysmectogenic properties. There is thus a demand for highly nematogeniccompounds having low values for the vapor pressure.

In particular in displays of the supertwist type (STN) having twistangles significantly greater than 220° or in displays having an activematrix, the materials employed hitherto have disadvantages.

Like similar compounds known, for example, from GermanOffenlegungsschriften 26 36 684 and 29 07 332, these compounds of theformula I can be used as components of liquid-crystalline media, inparticular for displays based on the principle of the twisted cell.

All the substances employed hitherto for this purpose have certaindisadvantages, for example excessively high melting points, excessivelylow clear points, excessively low stability to the action of heat, lightor electrical fields, excessively low electrical resistance, excessivelyhigh temperature dependence of the threshold voltage, and unfavorabledielectric and/or elastic properties. The invention had the object offinding novel liquid-crystalline compounds which are suitable ascomponents of liquid-crystalline media, in particular for nematic mediahaving a positive dielectric anisotropy, and which do not have thedisadvantages of the known compounds, or only do so to a lesser extent.This object has been achieved by the provision of the novel compounds ofthe formula I.

It has been found that the compounds of the formula I are preeminentlysuitable as components of liquid-crystalline media. In particular, theycan be used to obtain liquid-crystalline media having broad nematicranges, excellent nematogeneity down to low temperatures, excellentchemical stability, pronounced ε⊥ with a positive dielectric anisotropy,low temperature dependence of the threshold voltage and/or low opticalanisotropy. In addition, the novel compounds have good solubility forother components of media of this type and a high positive dielectricanisotropy with, at the same time, favorable viscosity and excellentelastic properties. The compounds of the formula I facilitate both STNdisplays having a very steep electrooptical characteristic line anddisplays having an active matrix with excellent long-term stability.

In the pure state, the compounds of the formula I are colorless and forma liquid-crystalline mesophase in a temperature range which is favorablylocated for electrooptical use.

The invention thus relates to the compounds of the formula I and to theuse of the compounds of the formula I as components ofliquid-crystalline media, to liquid-crystalline media containing atleast one compound of the formula I, and to electrooptical displayswhich contain media of this type.

Above and below, n, Q¹, Q², r, A, X, Y and Z are as defined above,unless expressly stated otherwise.

In the compounds of the formula I, the alkyl groups C_(n)H_(2n+1) arepreferably straight-chain. Accordingly, C_(n)H_(2n+1) is preferablymethyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl orlikewise preferably H. n is preferably 0, 1, 2, 3, 4 or 5.

Compounds of the formula I having branched alkyl groups may occasionallybe of importance due to better solubility in the customaryliquid-crystalline base materials, but in particular as chiral dopes ifthey are optically active. Branched groups of this type generallycontain not more than one chain branch. Preferred branched alkylradicals are isopropyl, 2-butyl (=1-methylpropyl), isobutyl(=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methylbutyl),2-methylpentyl, 3-methylpentyl, 2-heptyl (=1-methylhexyl), 2-octyl(=2-methylheptyl) and 2-ethylhexyl.

X is preferably F, Cl, —CF₃, OCHF₂ or —OCF₃. X is furthermore preferablyCN, in particular if simultaneously Z=F and Y=F or H. in particular Y=F.Very particular preference is given to compounds where X=CF₃, —OCF₃ or—OCHF₂.

r is preferably 1, 2 or 3 or furthermore preferably 0. A is preferably asingle bond and furthermore preferably trans-1,4-cyclohexylene or1,4-phenylene. In the case where Q¹=Q²=H; r=2 or 3, Z=H, X=F or Cl andsimultaneously Y=F or H, A is preferably a single bond, 1,4-phenylene or3-fluoro-1,4-phenylene.

In addition, the compounds of the formula I are prepared by methodsknown per se, as described in the literature (for example in thestandard works, such as Houben-Weyl, Methoden der Organischen Chemie[Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to beprecise under reaction conditions which are known and suitable for thereactions mentioned. Use may also be made here of variants which areknown per se, but are not described in greater detail.

If desired, the starting materials can also be formed in situ, by notisolating them from the reaction mixture but instead immediatelyreacting them further to form the compounds of the formula I.

Preferably, an aldehyde of the formula II

in which X, Y and Z are as defined above, is converted into compounds ofthe formula I by the Wittig method using an appropriate phosphoniumsalt.

Some of the starting materials and the reactive derivatives thereof areknown, and some can be prepared without difficulty from compounds knownfrom the literature by standard methods of organic chemistry. Forexample, the precursors of the formula II which are suitable for thesynthesis can be obtained by the following synthetic scheme:

The Grignard compound obtained from the corresponding bromobenzenederivative is reacted with chlorotrialkyl orthotitanate or -zirconate bythe method of WO 87/05599 to give the tertiary cyclohexanol. Eliminationof water, hydrogenation of the double bond and isomerization give thetrans-cyclohexanecarboxylate by customary methods. From the latter, thesuitable precursors of the formula II are obtained by customary standardmethods.

A possible synthesis of compounds where A=trans-1,4-cyclohexylene or1,4-phenylene is given in the following scheme:

Homologization of the cyclohexanecarboxylic acids or the correspondingaldehydes gives the compounds according to the invention completelyanalogously to the synthesis schemes given above.

The compounds of the formula I where A=3-fluoro-1,4-phenylene areincreased [sic] entirely analogously to the first synthesis scheme(preparation of compounds where A=a single bond) by using

in place of the bromobenzene derivative. The bromobiphenyl compound can,be prepared in a manner known per se by coupling reactions catalyzed bytransition metals (E. Poetsch, Kontakte (Darmstadt) 1988 (2), p. 15).

It is obvious to a person skilled in the art that the abovementionedsynthetic methods can also be modified in that the syntheses describedare carried out using precursors in which the radical X is replaced by agroup, which can be converted into X. For example, ether cleavage ofalkoxy compounds gives the corresponding phenols, from which the OCF₃and OCF₂H compounds can be prepared by routine methods by reaction withCCl₄/HF or CClF₂H/NaOH. The corresponding benzoic acids can be used toprepare the nitriles or the CF₃ compounds by treatment with SF₄.

However, it often proves advantageous to react a phosphonium salt of theformula III

with an appropriate aldehyde by the Wittig method. The compounds of theformula III are obtained from the above-described cyclohexylmethylalcohols by the following scheme:

Homologization gives the corresponding higher phosphonium salts:

Homologization by one carbon atom is best carried out via the nitriles:

In the case of base-sensitive nitriles, the conversion to the alcohol isbest carried out by reducing the nitrile to the aldehyde using DIBAH andsubsequently to the alcohol using LiAlH₄.

The corresponding iodides are obtained from the alcohols via thetosylates by the Finkelstein method; the iodides are then converted intothe corresponding phosphonium salts by boiling in acetonitrilecontaining PPh₃.

The ylides derived from these phosphonium salts (and prepared bytreatment with n-BuLi in hexane at −70° C. with exclusion of oxygen)react with aldehydes to give cis-olefins. These cis-olefins are thenisomerized by the phosphorus-betaine method of E. Vedejs and P. C. Fuchs(JACS 95 822 (1973)) to give the trans-olefins.

In the case where Q²=CH₃, n is preferably 0. To synthesize thesepreferred compounds, a carboxylic acid of the formula II′ is preferablyreacted with 2 equivalents of MeLi to give III′, from which a compoundof the formula I according to the invention is obtained by the Wittigmethod:

Some of the starting materials of the formula II′ and the reactivederivatives thereof are known, and some can be prepared withoutdifficulties from compounds known from the literature by standardmethods of organic chemistry. For example, carboxylic acids of theformula II′ can be obtained by the following synthetic schemes:

The carboxylic acids mentioned can be converted into the higher homologs(r=1-5) by customary homologization reactions.

In the case where Q¹=CH₃, n is preferably 1. To synthesize thesepreferred compounds, a phosphonium salt of the formula II″ is preferablyreacted with acetone by the Wittig method in the presence of a base (forexample BuLi) to give a compound according to the invention.

Some of the starting materials of the formula II″ are known, and somecan be prepared without difficulties from compounds known from theliterature by standard methods of organic chemistry. For example,precursors of the compounds of the formula II″ can be obtained by thefollowing synthetic schemes:

The carboxylic acids mentioned can be converted, if desired, into thehigher homologs (r=1 to 5) by customary homologization reactions.

After reduction of the carboxylic acids obtained into the correspondingalcohols and conversion into the bromides or iodides, the phoshonium[sic] salts of the formula II″ are obtained therefrom by routinemethods.

The liquid-crystalline media according to the invention preferablycontain 2 to 40, in particular 4 to 30, components as furtherconstituents besides one or more compounds according to the invention.These media very particularly preferably contain 7 to 25 componentsbesides one or more compounds according to the invention. These furtherconstituents are preferably selected from nematic or nematogenic(monotropic or isotropic) substances, in particular substances from theclasses of the biphenyls, terphenyls, phenyl or cyclohexyl benzoates,phenyl or cyclohexyl esters of cyclohexanecarboxylic acid, phenyl orcyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl estersof cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters ofbenzoic acid, of cyclohexanecarboxylic acid and ofcyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexenes,cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes,4,4′-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl-or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- orcyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cyclohexylethanes,1-cyclohexyl-2-(4-phenylcyclohexyl)-ethanes,1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes andtolans. The 1,4-phenylene groups in these compounds may also befluorinated.

The most important compounds suitable as further constituents of mediaaccording to the invention can be characterized by the formulae 1, 2, 3,4 and 5:R′-L-E-R″  1 R′-L-COO-E-R″  2R′-L-OOC-E-R″  3R′-L-CH₂CH₂-E-R″  4R′-L-CC-E-R″  5

In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical ordifferent, are in each case independently of one another, a bivalentradical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-,-Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images,where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc istrans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr ispyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyland G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl,pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

One of the radicals L and E is preferably Cyc, Phe or Pyr. E ispreferably Cyc, Phe or Phe-Cyc. The media according to the inventionpreferably contain one or more components selected from the compounds ofthe formulae 1, 2, 3, 4 and 5 in which L and E are selected from thegroup comprising Cyc, Phe and Pyr and simultaneously one or morecomponents selected from the compounds of the formulae 1, 2, 3, 4 and 5in which one of the radicals L and E is selected from the groupcomprising Cyc, Phe and Pyr and the other radical is selected from thegroup comprising -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-,and optionally one or more components selected from the compounds of theformulae 1, 2, 3, 4 and 5 in which the radicals L and E are selectedfrom the group comprising -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.

In the compounds of the subformulae 1a, 2a, 3a, 4a and 5a, R′ and R″ arein each case, independently of one another, alkyl, alkenyl, alkoxy,alkenyloxy or alkanoyloxy having up to 8 carbon atoms. In most of thesecompounds, R′ and R″ are different from one another, one of theseradicals usually being alkyl or alkenyl. In the compounds of thesubformulae 1b, 2b, 3b, 4b and 5b, R″ is —CN, —CF₃, —OCF₃, —OCHF₂, F, Clor —NCS; in this case, R has the meaning given for the compounds of thesub-formulae 1a to 5a and is preferably alkyl or alkenyl. R″ ispreferably selected from the group comprising —F, Cl, —CF₃, —OCHF₂ and—OCF₃. However, other variants of the proposed substituents in thecompounds of the formulae 1, 2, 3, 4 and 5 are common. Many suchsubstances or alternatively mixtures thereof are commercially available.All these substances can be obtained by methods which are known from theliterature or analogously thereto.

Besides components from the group comprising the compounds 1a, 2a, 3a,4a and 5a (Group 1), the media according to the invention preferablyalso contain components from the group comprising the compounds 1b, 2b,3b, 4b and 5b (Group 2), whose proportions are preferably as follows:

-   Group 1: 20 to 90%, in particular 30 to 90%, Group 2: 10 to 80%, in    particular 10 to 50%,-   the sum of the proportions of the compounds according to the    invention and of the compounds from Groups 1 and 2 adding up to    100%.

The media according to the invention preferably contain 1 to 40%, inparticular preferably 5 to 30%, of compounds according to the invention.Further preferred media are those which contain more than 40%, inparticular 45 to 90%, of compounds according to the invention. The mediapreferably contain three, four or five compounds according to theinvention.

The media according to the invention are prepared in a manner which iscustomary per se. In general, the components are dissolved in oneanother, expediently at elevated temperature. By means of suitableadditives, the liquid-crystalline phases can be modified in accordancewith the invention in a manner such that they can be used in all typesof liquid-crystal display elements which have hitherto been disclosed.

Additives of this type are known to those skilled in the art and aredescribed in detail in the literature (H. Kelker/R. Hatz, Handbook ofLiquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroicdyes can be added for the production of colored guest-host systems, orsubstances can be added to modify the dielectric anisotropy, theviscosity and/or the orientation of the nematic phases.

In particular, the media according to the invention are suitable for usein MLC displays.

The examples below are intended to illustrate the invention withoutrepresenting a limitation. mp.=melting point, cp.=clear point. Above andbelow, percentages are percent by weight; all temperatures are indicatedin degrees Celsius. “Customary work-up” means that water is added, themixture is extracted with methylene chloride, and the organic phase isseparated off, dried and evaporated, and the product is purified bycrystallization and/or chromatography.

In addition, the abbreviations have the following meanings:

-   C: crystalline-solid state, S: smectic phase (the index    characterizes the phase type), N: nematic state, Ch: cholesteric    phase, I: isotropic phase. The number between two symbols indicates    the conversion temperature in degrees Celsius.

DAST Diethylaminosulfur trifluoride DCC Dicyclohexylcarbodiimide DDQDichlorodicyanobenzoquinone DIBALH Diisobutylaluminum hydride DMSODimethyl sulfoxide POT Potassium tertiary-butanolate THF TetrahydrofuranpTSOH p-Toluenesulfonic acid

EXAMPLE 1

One equivalent of potassium t-butylate is added to a mixture oftrans-4-(3,4-difluorophenyl)cyclohexane-carbaldehyde andpropyltriphenylphosphonium bromide in n-butanol, and the mixture issubjected to customary work-up, to give4-trans-4-(1-butenyl)cyclohexyl-1,2-difluoro-benzene.

EXAMPLE 2

A mixture of2-trans-4-(p-trifluoromethoxy-phenyl)cyclohexylethyltriphenylphosphoniumiodide and propanal in hexane is treated with butyllithium, and themixture is subjected to customary work-up. The4-trans-4-(cis-2-pentenyl)cyclohexyltrifluoromethoxybenzene obtained isepoxidized using m-chloroperbenzoic acid. 4.15 ml of a 1.15 M solutionof lithium diphenylphosphide in THF are added at 25° C. to a solution ofthe epoxide obtained (0.005 mol) in 15 ml of THF with extremely carefulexclusion of atmospheric oxygen.

Disappearance of the red color of the phosphide is awaited, and 1.5equivalents of freshly distilled methyl iodide are then added to thereaction mixture (likewise at 25° C.). After 2 hours, the mixture issubjected to aqueous work-up. The organic phase is separated off,filtered through silica gel and subsequently evaporated. The residue ispurified by chromatography and crystallization, to give4-trans-4-(trans-2-pentenyl)cyclohexyltrifluoromethoxybenzene.

EXAMPLES 3 to 146

The following compounds of the formula I are obtained analogously toExample 1 or 2 from the corresponding aldehydes:

n r X Y Z A  (3) 3 0 F F H ‘—’  (4) 2 1 F F H ‘—’  (5) 0 2 F F H ‘—’ (6) 1 2 F F H ‘—’  (7) 3 2 F F H ‘—’  (8) 0 0 F H H ‘—’  (9) 1 0 F H H‘—’ (10) 0 2 F H H ‘—’ (11) 1 2 F H H ‘—’ (12) 3 2 F H H ‘—’ (13) 0 0 ClH H ‘—’ (14) 1 0 Cl H H ‘—’ (15) 0 2 Cl H H ‘—’ (16) 1 2 Cl H H ‘—’ (17)3 2 Cl H H ‘—’ (18) 0 0 Cl F H ‘—’ (19) 1 0 Cl F H ‘—’ (20) 0 2 Cl F H‘—’ (21) 1 2 Cl F H ‘—’ (22) 3 2 Cl H H ‘—’ (23) 0 0 —CF₃ H H ‘—’ (24) 10 —CF₃ H H ‘—’ (25) 0 2 —CF₃ H H ‘—’ (26) 1 2 —CF₃ H H ‘—’ (27) 3 2 —CF₃H H ‘—’ (28) 0 0 —OCF₃ H H ‘—’ (29) 1 0 —OCF₃ H H ‘—’ (30) 0 2 —OCF₃ H H‘—’ (31) 1 2 —OCF₃ H H ‘—’ (32) 3 2 —OCF₃ H H ‘—’ (33) 0 0 —OCHF₃ H H‘—’ (34) 1 2 —OCHF₃ H H ‘—’ (35) 0 2 —OCHF₃ H H ‘—’ (36) 1 2 —OCHF₃ H H‘—’ (37) 3 2 —OCHF₃ H H ‘—’ (38) 0 0 —CN F H ‘—’ (39) 1 0 —CN F H ‘—’(40) 0 2 —CN F H ‘—’ (41) 1 2 —CN F H ‘—’ (42) 3 2 —CN F H ‘—’ (43) 0 0—CN F  F^(x) ‘—’ (44) 1 0 —CN F  F^(x) ‘—’ (45) 0 2 —CN F  F^(x) ‘—’(46) 1 2 —CN F  F^(x) ‘—’ (47) 3 2 —CN F  F^(x) ‘—’ ^(x)Z in theortho-position to X

n r X Y Z A (57) 3 0 F F H Cyc (58) 2 1 F F H Cyc (59) 0 2 F F H Cyc(60) 1 2 F F H Cyc (61) 3 2 F F H Cyc (62) 0 0 F H H Cyc (63) 1 0 F H HCyc (64) 0 2 F H H Cyc (65) 1 2 F H H Cyc (66) 3 2 F H H Cyc (67) 0 0 ClH H Cyc (68) 1 0 Cl H H Cyc (69) 0 2 Cl H H Cyc (70) 1 2 Cl H H Cyc (71)3 2 Cl H H Cyc (72) 0 0 Cl F H Cyc (73) 1 0 Cl F H Cyc (74) 0 2 Cl F HCyc (75) 1 2 Cl F H Cyc (76) 3 2 Cl F H Cyc (77) 0 0 —CF₃ H H Cyc (78) 10 —CF₃ H H Cyc (7)  0 2 —CF₃ H H Cyc (80) 1 2 —CF₃ H H Cyc (81) 3 2 —CF₃H H Cyc (82) 0 0 —OCF₃ H H Cyc (83) 1 0 —OCF₃ H H Cyc (84) 0 2 —OCF₃ H HCyc (85) 1 2 —OCF₃ H H Cyc (86) 3 2 —OCF₃ H H Cyc (87) 0 0 —OCHF₃ H HCyc (88) 1 0 —OCHF₃ H H Cyc (89) 0 2 —OCHF₂ H H Cyc (90) 1 2 —OCHF₂ H HCyc (91) 3 2 —OCHF₂ H H Cyc (92) 0 0 —CN F H Cyc (93) 1 0 —CN F H Cyc(94) 0 2 —CN F H Cyc (95) 1 2 —CN F H Cyc (96) 3 2 —CN F H Cyc (97) 0 0—CN F  F^(x) Cyc (98) 1 0 —CN F  F^(x) Cyc (99) 0 2 —CN F  F^(x) Cyc(100)  1 2 —CN F  F^(x) Cyc (101)  3 2 —CN F  F^(x) Cyc ^(x)Z in theortho-position to X

n r X Y Z A (102) 3 0 F F H Phe (103) 2 1 F F H Phe (104) 0 2 F F H Phe(105) 1 2 F F H Phe (106) 3 2 F F H Phe (107) 0 0 F H H Phe (108) 1 0 FH H Phe (109) 0 2 F H H Phe (110) 1 2 F H H Phe (111) 3 2 F H H Phe(112) 0 0 Cl H H Phe (113) 1 0 Cl H H Phe (114) 0 2 Cl H H Phe (115) 1 2Cl H H Phe (116) 3 2 Cl H H Phe (117) 0 0 Cl F H Phe (118) 1 0 Cl F HPhe (119) 0 2 Cl F H Phe (120) 1 2 Cl F H Phe (121) 3 2 Cl F H Phe (122)0 0 —CF₃ H H Phe (123) 1 0 —CF₃ H H Phe (124) 0 2 —CF₃ H H Phe (125) 1 2—CF₃ H H Phe (126) 3 2 —CF₃ H H Phe (127) 0 0 —OCF₃ H H Phe (128) 1 0—OCF₃ H H Phe (129) 0 2 —OCF₃ H H Phe (130) 1 2 —OCF₃ H H Phe (131) 3 2—OCF₃ H H Phe (132) 0 0 —OCHF₂ H H Phe (133) 1 0 —OCHF₂ H H Phe (134) 02 —OCHF₂ H H Phe (135) 1 2 —OCHF₂ H H Phe (136) 3 2 —OCHF₂ H H Phe (137)0 0 —CN F H Phe (138) 1 0 —CN F H Phe (139) 0 2 —CN F H Phe (140) 1 2—CN F H Phe (141) 3 2 —CN F H Phe (142) 0 0 —CN F  F^(x) Phe (143) 1 0—CN F  F^(x) Phe (144) 0 2 —CN F  F^(x) Phe (145) 1 2 —CN F  F^(x) Phe(146) 3 2 —CN F  F^(x) Phe ^(x)Z in the ortho-position to X

EXAMPLE 147

Reaction of methyl 3-[trans-4-(p-fluorophenyl)cyclohexyl]propyl ketonewith methylphosphonium iodide and butyllithium by the Wittig method withcustomary work-up and purification by chromatography givestrans-1-p-fluorophenyl-4-(4-methylpenten-4-yl)cyclohexane.

EXAMPLES 148 to 249

The following compounds (n=0, Q¹=H, Q=CH₃) are obtained analogously toExample 1 from the corresponding aldehydes:

r X Y Z A (148) 0 F H H ‘—’ (149) 1 F H H ‘—’ (150) 2 F H H ‘—’ (151) 4F H H ‘—’ (152) 0 F F H ‘—’ (153) 1 F F H ‘—’ (154) 2 F F H ‘—’ (155) 3F F H ‘—’ (156) 4 F F H ‘—’ (157) 5 F F H ‘—’ (158) 0 Cl H H ‘—’ (159) 1Cl H H ‘—’ (160) 2 Cl H H ‘—’ (161) 3 Cl H H ‘—’ (162) 4 Cl H H ‘—’(163) 5 Cl H H ‘—’ (164) 0 Cl F H ‘—’ (165) 1 Cl F H ‘—’ (166) 2 Cl F H‘—’ (167) 3 Cl F H ‘—’ (168) 4 Cl F H ‘—’ (169) 5 Cl F H ‘—’ (170) 0 CF₃H H ‘—’ (171) 1 CF₃ H H ‘—’ (172) 2 CF₃ H H ‘—’ (173) 3 CF₃ H H ‘—’(174) 4 CF₃ H H ‘—’ (175) 5 CF₃ H H ‘—’ (176) 0 OCF₃ H H ‘—’ (177) 1OCF₃ H H ‘—’ (178) 2 OCF₃ H H ‘—’ (179) 0 OCHF₂ H H ‘—’ (180) 1 OCHF₂ HH ‘—’ (181) 2 OCHF₂ H H ‘—’ (182) 0 F H H Cyc (183) 1 F H H Cyc (184) 2F H H Cyc (185) 3 F H H Cyc (186) 0 F F H Cyc (187) 1 F F H Cyc (188) 2F F H Cyc (189) 3 F F H Cyc (190) 4 F F H Cyc (191) 5 F F H Cyc (192) 0Cl H H Cyc (193) 1 Cl H H Cyc (194) 2 Cl H H Cyc (195) 3 CI H H Cyc(196) 4 Cl H H Cyc (197) 5 Cl H H Cyc (198) 0 Cl F H Cyc (199) 1 Cl F HCyc (200) 2 Cl F H Cyc (201) 3 Cl F H Cyc (202) 4 Cl F H Cyc (203) 5 ClF H Cyc (204) 0 CF₃ H H Cyc (205) 1 CF₃ H H Cyc (206) 2 CF₃ H H Cyc(207) 3 CF₃ H H Cyc (208) 4 CF₃ H H Cyc (209) 5 CF₃ H H Cyc (210) 1 OCF₃H H Cyc (211) 2 OCF₃ H H Cyc (212) 3 OCF₃ H H Cyc (213) 0 OCHF₂ H H Cyc(214) 1 OCHF₂ H H Cyc (215) 2 OCHF₂ H H Cyc (216) 0 F H H Phe (217) 1 FH H Phe (218) 2 F H H Phe (219) 3 F H H Phe (220) 0 F F H Phe (221) 1 FF H Phe (222) 2 F F H Phe (223) 3 F F H Phe (224) 4 F F H Phe (225) 5 FF H Phe (226) 0 Cl H H Phe (227) 1 Cl H H Phe (228) 2 Cl H H Phe (229) 3Cl H H Phe (230) 4 Cl H H Phe (231) 5 Cl H H Phe (232) 0 Cl F H Phe(233) 1 Cl F H Phe (234) 2 Cl F H Phe (235) 3 Cl F H Phe (236) 4 Cl F HPhe (237) 5 Cl F H Phe (238) 0 CF₃ H H Phe (239) 1 CF₃ H H Phe (240) 2CF₃ H H Phe (241) 3 CF₃ H H Phe (242) 4 CF₃ H H Phe (243) 5 CF₃ H H Phe(244) 1 OCF₃ H H Phe (245) 2 OCF₃ H H Phe (246) 3 OCF₃ H H Phe (247) 1OCHF₂ H H Phe (248) 2 OCHF₂ H H Phe (249) 3 OCHF₂ H H Phe

EXAMPLE 250

Reaction of 2-trans-4-(p-fluorophenyl)cyclohexyl]ethylphosphonium [sic]iodide with acetone and butyllithium by the Wittig method with customarywork-up and purification by chromatography givestrans-1-p-fluorophenyl-4-(4-methylpenten-3-yl)cyclohexane.

EXAMPLES 251-352

The following compounds (n=1, Q¹=CH₃. Q²=H) are obtained analogously toExample 250 from the corresponding aldehydes:

r X Y Z A (251) 0 F H H ‘—’ (252) 1 F H H ‘—’ (253) 2 F H H ‘—’ (254) 4F H H ‘—’ (255) 0 F F H ‘—’ (256) 1 F F H ‘—’ (257) 2 F F H ‘—’ (258) 3F F H ‘—’ (259) 4 F F H ‘—’ (260) 5 F F H ‘—’ (261) 0 Cl H H ‘—’ (262) 1Cl H H ‘—’ (263) 2 Cl H H ‘—’ (264) 3 Cl H H ‘—’ (265) 4 Cl H H ‘—’(266) 5 Cl H H ‘—’ (267) 0 Cl F H ‘—’ (268) 1 Cl F H ‘—’ (269) 2 Cl F H‘—’ (270) 3 Cl F H ‘—’ (271) 4 Cl F H ‘—’ (272) 5 Cl F H ‘—’ (273) 0 CF₃H H ‘—’ (274) 1 CF₃ H H ‘—’ (275) 2 CF₃ H H ‘—’ (276) 3 CF₃ H H ‘—’(277) 4 CF₃ H H ‘—’ (278) 5 CF₃ H H ‘—’ (279) 0 OCF₃ H H ‘—’ (280) 1OCF₃ H H ‘—’ (281) 2 OCF₃ H H ‘—’ (282) 0 OCHF₂ H H ‘—’ (283) 1 OCHF₂ HH ‘—’ (284) 2 OCHF₂ H H ‘—’ (285) 0 F H H Cyc (286) 1 F H H Cyc (287) 2F H H Cyc (288) 3 F H H Cyc (289) 0 F F H Cyc (290) 1 F F H Cyc (291) 2F F H Cyc (292) 3 F F H Cyc (293) 4 F F H Cyc (294) 5 F F H Cyc (295) 0Cl H H Cyc (296) 1 Cl H H Cyc (297) 2 Cl H H Cyc (298) 3 Cl H H Cyc(299) 4 Cl H H Cyc (300) 5 Cl H H Cyc (301) 0 Cl F H Cyc (302) 1 Cl F HCyc (303) 2 Cl F H Cyc (304) 3 Cl F H Cyc (305) 4 Cl F H Cyc (306) 5 ClF H Cyc (307) 0 CF₃ H H Cyc (308) 1 CF₃ H H Cyc (309) 2 CF₃ H H Cyc(310) 3 CF₃ H H Cyc (311) 4 CF₃ H H Cyc (312) 5 CF₃ H H Cyc (313) 1 OCF₃H H Cyc (314) 2 OCF₃ H H Cyc (315) 3 OCF₃ H H Cyc (316) 0 OCHF₂ H H Cyc(317) 1 OCHF₂ H H Cyc (318) 2 OCHF₂ H H Cyc (319) 0 F H H Phe (320) 1 FH H Phe (321) 2 F H H Phe (322) 3 F H H Phe (323) 0 F F H Phe (324) 1 FF H Phe (325) 2 F F H Phe (326) 3 F F H Phe (327) 4 F F H Phe (328) 5 FF H Phe (329) 0 Cl H H Phe (330) 1 Cl H H Phe (331) 2 Cl H H Phe (332) 3Cl H H Phe (333) 4 Cl H H Phe (334) 5 Cl H H Phe (335) 0 Cl F H Phe(336) 1 Cl F H Phe (337) 2 Cl F H Phe (338) 3 Cl F H Phe (339) 4 Cl F HPhe (340) 5 Cl F H Phe (341) 0 CF₃ H H Phe (342) 1 CF₃ H H Phe (343) 2CF₃ H H Phe (344) 3 CF₃ H H Phe (345) 4 CF₃ H H Phe (346) 5 CF₃ H H Phe(347) 1 OCF₃ H H Phe (348) 2 OCF₃ H H Phe (349) 3 OCF₃ H H Phe (350) 1OCHF₂ H H Phe (351) 2 OCHF₂ H H Phe (352) 3 OCHF₂ H H Phe

The following are examples of media containing at least one compound ofthe formula I:

EXAMPLE A

A mixture comprising

-   7% of p-(trans-4-propylcyclohexyl)benzonitrile,-   5% of    4-[trans-4-(trans-2-pentenyl)cyclohexyl]trifluoromethoxybenzene,-   24% of p-(trans-4-pentylcyclohexyl)fluorobenzene,-   14% of p-(trans-4-heptylcyclohexyl)fluorobenzene,-   15% of    2-[trans-4-(3,4-difluorophenyl)cyclohexyl]-5-butyl-1,3-dioxane,-   18% of 2-[trans-4-(p-fluorophenyl)cyclohexyl]-5-ethyl-1,3-dioxane,    and-   17% of 2-[trans-4-(p-fluorophenyl)cyclohexyl]-5-propyl-1,3-dioxane-   has a high electrical resistance.

1. A phenylcyclohexane of formula I

in which n is 0 to 7, Q¹ and Q² are H, or one of these radicals isalternatively CH₃, r is 0, 1, 2, 3, 4 or 5, A istrans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or asingle bond, X is —CN, and Y and Z are each, independently of oneanother, H or F, with the proviso that, in the case where A istrans-1,4-cyclohexylene or a single bond, Q¹=Q²=H and simultaneouslyX=CN, Y and Z are F.
 2. A liquid-crystalline medium comprising at leasttwo liquid-crystalline components, wherein at least one component is aphenylcyclohexane of formula I according to claim
 1. 3. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 2. 4. Aphenylcyclohexane according to claim 1, wherein Q¹ and Q² are H and A istrans-1,4-cyclohexylene.
 5. A phenylcyclohexane according to claim 1,wherein n is
 0. 6. A phenylcyclohexane according to claim 1, wherein nis
 1. 7. A liquid-crystalline medium comprising at least twoliquid-crystalline components, wherein at least one component is aphenylcyclohexane of formula I according to claim
 4. 8. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 7. 9. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is a phenylcyclohexane offormula I according to claim
 5. 10. An electrooptical display based on aliquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim
 9. 11. A liquid-crystalline medium comprising atleast two liquid-crystalline components, wherein at least one componentis a phenylcyclohexane of formula I according to claim
 6. 12. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 11. 13. Aphenylcyclohexane of formula I

in which n is 0 to 7, Q¹ and Q² are H, or one of these radicals isalternatively CH₃, r is 0, 1, 2, 3, 4 or 5, A istrans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or asingle bond, X is F, Cl, —CF₃ or —OCF₃ and Y and Z are eachindependently H or F.
 14. A phenylcyclohexane according to claim 13,wherein Q¹ and Q² are H and A is trans-1,4-cyclohexylene.
 15. Aphenylcyclohexane according to claim 13, wherein n is
 0. 16. Aphenylcyclohexane according to claim 13, wherein n is
 1. 17. Aphenylcyclohexane according to claim 13, wherein X and Y are F and Z isH.
 18. A phenylcyclohexane according to claim 13, wherein Z is F.
 19. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is a phenylcyclohexane offormula I according to claim
 13. 20. An electrooptical display based ona liquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim
 19. 21. A liquid-crystalline medium comprising atleast two liquid-crystalline components, wherein at least one componentis a phenylcyclohexane of formula I according to claim
 14. 22. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 21. 23. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is a phenylcyclohexane offormula I according to claim
 15. 24. An electrooptical display based ona liquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim
 23. 25. A liquid-crystalline medium comprising atleast two liquid-crystalline components, wherein at least one componentis a phenylcyclohexane of formula I according to claim
 16. 26. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 25. 27. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is a phenylcyclohexane offormula I according to claim
 17. 28. An electrooptical display based ona liquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim
 27. 29. A liquid-crystalline medium comprising atleast two liquid-crystalline components, wherein at least one componentis a phenylcyclohexane of formula I according to claim
 18. 30. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 29. 31. Aphenylcyclohexane of formula I

in which n is 0 to 7, Q¹ and Q² are H, or one of these radicals isalternatively CH₃, r is 0, 1, 2 or 3, A is trans-1,4-cyclohexylene,1,4-phenylene,3-fluoro-1,4-phenylene or a single bond, X is F, and Y andZ are each independently H or F.
 32. A phenylcyclohexane according toclaim 31, wherein Q¹ and Q² are H and A is trans-1,4-cyclohexylene. 33.A phenylcyclohexane according to claim 31, wherein n is
 0. 34. Aphenylcyclohexane according to claim 31, wherein n is
 1. 35. Aphenylcyclohexane according to claim 31, wherein X and Y are F and Z isH.
 36. A phenylcyclohexane according to claim 31, wherein Z is F.
 37. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is a phenylcyclohexane offormula I according to claim
 31. 38. An electrooptical display based ona liquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim
 37. 39. A liquid-crystalline medium comprising atleast two liquid-crystalline components, wherein at least one componentis a phenylcyclohexane of formula I according to claim
 32. 40. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 39. 41. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is a phenylcyclohexane offormula I according to claim
 33. 42. An electrooptical display based ona liquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim
 41. 43. A liquid-crystalline medium comprising atleast two liquid-crystalline components, wherein at least one componentis a phenylcyclohexane of formula I according to claim
 34. 44. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 43. 45. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is a phenylcyclohexane offormula I according to claim
 35. 46. An electrooptical display based ona liquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim
 45. 47. A liquid-crystalline medium comprising atleast two liquid-crystalline components, wherein at least one componentis a phenylcyclohexane of formula I according to claim
 36. 48. Anelectrooptical display based on a liquid-crystal cell, wherein theliquid-crystal cell contains a medium according to claim
 47. 49. Aphenylcyclohexane according to claim 1, wherein Z is ortho to X.
 50. Aliquid-crystalline medium comprising at least two liquid-crystallinecomponents, wherein at least one component is phenylcyclohexane offormula I according to claim
 49. 51. An electrooptical display based ona liquid-crystal cell, wherein the liquid-crystal cell contains a mediumaccording to claim 50.